That's a lot of buttons for sure. Have fun going through them.
I washed all my Grams' buttons this spring after having been stored for over 40 years. Also my moms. Just filled the sink with hot water and Dawn, took out all the metal buttons and threads, and placed the buttons in a strainer and dipped up and down several times, then let them sit for about 10 minutes. Rinsed and laid on a dish towel to dry. Clean, shiny, pretty buttons.